1. Field of the Invention
The present invention relates to removing offensive odors from cork. Specifically, the present invention relates to removing 2,4,6-trichloroanisole (TCA) which has a characteristic odor.
2. Description of the Background Art
Cork has unique characteristics. It is lightweight and has a high degree of resilience. Additionally, it has excellent gas and liquid sealing properties, and has stability against solvents such as alcohol. Furthermore, it is a hygienic material which is food-safe and not harmful to human beings, and has no intrinsic odor.
Because of the above mentioned characteristics, cork has been widely utilized as stoppers for casings such as bottles filled with liquor such as wine, brandy or whiskey, or casings packed with various kinds of foods.
However, in spite of having no intrinsic odor, offensive odor is encountered on cork stoppers on rare occasions. This odor, when present, deteriorates the quality of the contents of the bottles or casings sealed by the cork. Recently, by various studies, 2,4,6-trichloroanisol (TCA) has been identified as the substance which originates the offensive odor. TCA is considered as the substance produced by moulds from 2,4,6-trichlorophenol (TCP) which is utilized in agents conventionally used to spray cork oak. Also, in "Journal of Agricultural and Food Chemistry", (1982) pages 359 to 362, presumption is given that 2,4,6-trichlorophenol and other related chlorinated compounds originate from chlorination of a liquid-related substance during the chlorinate bleaching used in the processing of the cork and that these compounds are later extracted into the liquor, such as wine. Similar consideration that a clorinate agent is the source of the odor substance has been given in "Science des Ailments" (1984), pages 81 to 93. In the discussion, It has been pointed out that the 2,4,6-trichloroanisol is derived from pentachlorophenol or other chlorinated pesticides applied to the tree. Further consideration is given that cork material and corks stored in premises with an atmosphere polluted by chloroanisoles may contaminate bottled wine aged in healthy cellars.
Methods for effective deodorization of cork have been studied, and the following methods have been attempted.
(1) Dry-Heating Deodorization
Cork is heated and dried at 80.degree. C. for 6 to 8 hours, after which the offensive odor causing substances are substantially evaporated. However, TCA is specifically adsorbed by the macromolecular compounds which form cork such as cellulose, lignin and suberin, and it is difficult to remove TCA in the dried state. The boiling point of TCA is 240.degree. C. at 738.2 mmHg, and 132.degree. C. at 28 mmHg. Therefore, in order to evaporate TCA, a heating temperature must be applied which is higher than the boiling point of TCA. However, it is difficult to raise the internal temperature of cork without heating the surface excessively, which results in deterioration of cork's desirable characteristics. As such, heating is applied only to the surface of the cork, therefore TCA in the interior cannot be removed entirely.
(2) Repetition Heating Deodorization
Cork is heated at 80.degree. C. for 6 hours and is then left at room temperatures for about a month. TCA can be removed by repeating this treatment many times. However, this method requires long periods of treatment until the TCA is entirely removed; therefore, production efficiency is low. For example, 2 or 3, repetitions of the above treatment is insufficient for entirely removing TCA.
(3) Citric Acid Deodorization
Cork is deodorized by being soaked in a 3 vol % solution of citric acid for 3 to 5 min. However, the effects of this deodorization technique are retained only for a short period. That is because, as cork resists absorption of liquids, the citric acid solution cannot reach the cork interior. Therefore, since the deodorizing treatment affects only the cork surface, untreated TCA within the cork is moved to the cork surface with the elapse of time; thus, the offensive odor re-occurs.
(4) Oxidant Bath Deodorization
Cork is deodorized and sterilized by soaking in a 1 vol % solution of hydroperoxide (H.sub.2 O.sub.2). However similar problems are caused as in the case of citric acid deodorization.
(5) Alcohol Steam Deodorization
Cork is left and deodorized in an alcohol atmosphere at 18.degree. to 24.degree. C. for a month. However, this method encounters the same problems as methods (3) and (4).
(6) Hot Water Washing
Cork in the grain state is washed in hot water at a temperature of 60.degree. C. The treatment needs to be repeated 2 times. But, as TCA has a relatively strong affinity for cork, it is moved to and retained in the internal portions of the cork. According to this method, therefore, the deodorizing effect is still insufficient because the treatment affects only the cork surface.
(7) Soxhlet Extraction
TCA in the cork is extracted by a Soxhlet extractor at 45.degree. C. for 24 hours with n-pentane. By this method, TCA is entirely removed from both the surface and internal areas of the cork. However, the equipment is very expensive and production costs become very high. Furthermore, a certain degree of safety risk is encountered with this method.
(8) Dispersion
It has been considered to simply grind the cork into grains having a certain diameter, and then form it back into the desired form by pressing with adhesives. However, since TCA is merely dispersed in each grain, high improvement cannot be expected from this approach.
(9) Sterilization with Irradiation
"Deutsche Lebensmittel-Rundschau" (1984) Pages 204-207, is directed to sterilization with irradiation. That the mechanism of formation of cork taint in wines is discussed. The use of an irradiation process has been proposed for preventing microbial conversion from TCA, and thus achieving prevention of cork taint. However, this method cannot remove TCA residing within internal structure of the cork.
(10) Sterilization with Ozone
German Patent First Publication No. 34 05 422 discusses that cork is sterilized with ozonized water or an ozonized silicone emulsion, in which the ozonized concentration is Pl mg/l at a temperature lower than 30.degree. C.
However, this method encounters the same problems as methods (3) and (4).